VS2010 Mschart - how to determine visible points when zoomed?

I've got a databound chart thats all nice and zoomy etc and I've figured out how to get the index of the point nearest the cursor (going to use that to try and select the datarow the data came from).

What I can't seem to find is how to figure out the limits of the visible points (x axis) when the graph is zoomed (line graph btw).

The cursor_changed event tells me the cursor.NewPosition and it also has SelectionStart and end but I think that's unreleated to the IsUserSelectionEnabled style zooming as I always get NaN from those when I do a chart zoom.

So how do you go about finding what the range of points is that are visible on the chart?
Thanks!